Refrigerant powered valve for a geothermal power plant

ABSTRACT

A vapor expansion system includes a normally closed pneumatic valve between the evaporator and the turbine inlet, with the valve being selectively actuated by the flow of refrigerant vapor from the evaporator so as to enable opening the valve only during periods in which sufficient pressure has built up in the evaporator to properly operate the turbine. A bypass line has a normally open pneumatic valve with an actuator that is similarly caused to operate by pressurized refrigerant vapor from the evaporator. Both actuators are vented to the condenser such that the refrigerant vapor vented from the actuator does not escape to ambient.

TECHNICAL FIELD

This disclosure relates generally to geothermal power plants and, more particularly, to a method and apparatus for operating the turbine inlet and bypass valves thereof.

BACKGROUND OF THE DISCLOSURE

In order to effectively use geothermal energy such as that naturally occurring at various locations in the earth, a closed loop vapor expansion system, including an evaporator/boiler, a turbine, a condenser and a pump, are employed, with the heat from the geothermal source being applied to the evaporator/boiler to heat the working fluid prior to its flowing to the turbine for the purpose of generating electrical power. Most commonly, a refrigerant is used as the working fluid, and the system is known as an Organic Rankine Cycle System. One such system is shown and described in U.S. Pat. No. 7,174,716, assigned to the predecessor of the assignee of the present disclosure.

During periods in which the evaporator/boiler is either coming online or going off-line, such that the temperature of the working fluid is insufficient for driving the turbine, it is necessary to bypass the turbine and allow the working fluid to proceed directly from the evaporator to the condenser so that the closed loop circulation of the working fluid otherwise continues. Heretofore, a pneumatic power valve has been used for that purpose, with an outside pressurized gas source (normally either bottled nitrogen or compressed air) providing the power to operate the valves and with the gas then being vented to atmosphere. Adding a compressor or a bottled gas system to the site has caused problems in the past, primarily in connection with maintenance, reliability and cost. Further, with such a supplementary pressurized source, it was possible to operate the valves at times when the conditions were not favorable for proper turbine operation thereby possibly resulting in damage to the turbine rotor from entrained liquid. There are presently no electrical actuators available that are capable of meeting the requirements for such a function.

DISCLOSURE

In accordance with one aspect of the disclosure, provision is made to use the energy of the working fluid in the system to power the turbine inlet/bypass valves. This is accomplished by selectively connecting the valves to the evaporator/boiler by way of a regulator such that pressurized refrigerant is provided to operate the valves in a regulated manner.

In accordance with another aspect of the disclosure a normally open valve is used as a bypass valve and a normally closed valve is used as a turbine inlet valve. Thus the valves are not operable to direct working fluid to the turbine unless sufficient pressure exists in the evaporator to operate the valves.

By another aspect of the disclosure, the low pressure sides of the valve actuators are vented to the condenser such that the refrigerant remains in the closed loop system rather than entering the atmosphere.

While the present disclosure has been particularly shown and described with reference to a preferred mode as illustrated in the drawings, it will be understood by one skilled in the art that various changes in detail may be effected therein without departing from the spirit and scope of the disclosure as defined by the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a geothermal power plant with the present disclosure incorporated therein.

FIG. 2 is a schematic illustration of the actuator portion thereof.

FIGS. 3A and 3B are cross sectional views of the solenoid valve portion thereof, in non-energized and energized positions, respectively.

DETAILED DESCRIPTION OF THE DISCLOSURE

Shown in FIG. 1 is a geothermal power plant 11 which includes a turbine 12, a condenser 13, a pump 14 and an evaporator/boiler 16. The power plant 11 is designed to operate with an organic refrigerant, such as R245fa or the like as the working fluid which circulates serially through the system with refrigerant vapor from the evaporator 16 passing to the turbine for the purpose of driving a generator 17 to generate electrical power. The resulting lower energy vapor then passes to the condenser 13 with the resulting condensate then being pumped to the evaporator 16 by way of the pump 14.

The heat source 18 for the evaporator 16 may be of any suitable type such as a naturally occurring geothermal heat source, or a generated heat source such as the exhaust of a gas turbine engine. Similarly, a cooling source 19, such as a cooling tower or a chiller is provided for the purpose of providing cooling water to the condenser 13.

A turbine inlet valve 21 is provided in a primary flow path line 15 between the evaporator 16 and turbine inlet 22. The turbine inlet valve 21 is a normally closed pneumatic valve with an actuator 23 that is shown in FIG. 2 and described more fully hereinafter. The actuator 23 is made to operate only by way of a pressurized source, and this source, rather than being independent from the system as in the prior art, is the evaporator 16. That is, pressurized refrigerant vapor flows along line 24 to a pressure regulator 26 which is adapted to provide refrigerant vapor at a predetermined pressure, for example 80 psi. The pressure regulated flow of refrigerant vapor then flows along line 27 to a solenoid valve S₁, which in turn, is controlled by a control C. Thus when the solenoid valve S₁ is opened, the refrigerant vapor flows into the actuator 23 to open the normally closed pneumatic valve 21.

Fluidly connected to the primary flow path line 15 is a bypass line 28, leading to a normally open pneumatic valve 29 and then to line 31 leading to the condenser 13. The pneumatic valve 29 has a rack-and-pinion actuator 32 similar to the actuator 23 described hereinabove. The actuator 32 is pressurized by refrigerant from the regulator 26 flowing along line 33 to the solenoid valve S₂, which is controlled by the control C. Thus, the pneumatic valve 29 is normally open unless it is closed by way of the actuator 32 when receiving pressurized gas from the regulator 26 when the solenoid valve S₂ is opened.

The manner in which the valves 21 and 29 are operated by way of their respective actuators will now be described. During periods of start up and shut-down, when the pressure in the evaporator 16 is insufficient to drive the turbine 12, the pressure at the regulator 26 is at a reduced pressure, the solenoid valves S₁ and S₂ are closed, and the actuators 23 and 32 are non-operable. Thus, the normally closed pneumatic valve 21 is closed, and the normally open pneumatic valve 29 is open such that any vapor from the evaporator then flows along line 28, through the normally open pneumatic valve 29, through the line 31 to the condenser 13. When the pressure in the evaporator 16 is sufficient to operate the turbine, the pressure at the regulator 26 will be sufficient to operate the actuators 23 and 32, and the solenoid valves S₁ and S₂ are opened by the control C. The actuator 32 will then be caused to operate to close the pneumatic valve 29, and the actuator 23 will be caused to operate to open the pneumatic valve 21 such that the vapor from the evaporator 16 then flows through the pneumatic valve 21 and to the turbine inlet 22.

Referring now to FIGS. 2 and 3, the operation of the actuators and the solenoids valves will be described in greater detail. As will be seen in FIG. 2, the actuator 23 includes a pressurized section 34 and a vented section 36, with a sliding piston seal 37 therebetween. A return spring 38 biases the sliding piston 37 toward the pressurized section 34. When the pressurized section 34 is pressurized by admittance of refrigerant vapor from the solenoid valve S₁ the rack-and-pinion causes rotation within the actuator 23 to thereby actuate (i.e. open) the turbine inlet valve 21. As will be seen in FIGS. 1 and 2, the vented section 36 is fluidly connected by the line 39 to the condenser 13 so as to allow the rotation, while at the same time disposing of the refrigerant vapor by channeling it to the condenser 13 rather than to ambient. The actuator 32 operates in substantially the same manner to close the normally open pneumatic valve 29.

Shown in FIGS. 3A and 3B is a solenoid valve S₁ with the slide 41 being in a non-energized and in an energized position, respectively. That is, in FIG. 3A, the slider 41 is in a position at the left as shown such that the pressurized section of the actuator 44 is vented along line 42 to the condenser 13, while the pressurized source is isolated. When the solenoid valve S₁ is energized by moving the slider 41 to the right as shown in FIG. 3B, the pressure source is fluidly connected to the pressure section of the actuator, while the vent is isolated. The solenoid valve S₂ operates in substantially the same manner.

Although the present disclosure has been particularly shown and described with reference to a preferred embodiment as illustrated by the drawings, it will be understood by one skilled in the art that various changes in detail made be made thereto without departing from the scope of the disclosure as defined by the claims. 

1. A vapor expansion system of the type having in serial flow relationship a turbine, a condenser, a pump and an evaporator, comprising: a pneumatically actuated valve with an actuator moveable to a position for fluidly connecting the evaporator to a turbine inlet by way of said valve; a conduit which fluidly interconnects said evaporator to said actuator such that pressurized refrigerant from said evaporator is selectively caused to move said actuator to open said pneumatically actuated valve.
 2. A vapor expansion system as set forth in claim 1 wherein said pneumatically actuated valve is a normally closed valve.
 3. A vapor expansion system as set forth in claim 1 wherein said actuator includes a vented section and said vented section is fluidly connected to said condenser.
 4. A vapor expansion system as set forth in claim 1 and including a pressure regulator between said evaporator and said actuator so as to provide pressurized refrigerant to said actuator at a predetermined pressure level.
 5. A vapor expansion system as set forth in claim 1 and including a solenoid valve fluidly connected between said evaporator and said actuator.
 6. A vapor expansion system as set forth in claim 5 wherein solenoid valve is a three way valve with a vent port being fluidly connected to the condenser.
 7. A vapor expansion system as set forth in claim 1 wherein said actuator includes a spring for biasing a sliding piston in position.
 8. A vapor expansion system as set forth in claim 1 wherein said actuator is of the rack-and-pinion type.
 9. A vapor expansion system as set forth in claim 1 and including a bypass line for conducting the flow of refrigerant vapor around said turbine and to said condenser said bypass line having a pneumatic valve disposed therein.
 10. A vapor expansion system as set forth in claim 9 wherein said pneumatic valve is a normally open valve with an actuator fluidly connected to said evaporator.
 11. A method of controlling a vapor expansion system of the type having in serial flow relationship a turbine, a condenser, a pump and an evaporator, comprising the steps of: providing a pneumatically actuated valve with an actuator moveable to a position for fluidly connecting the evaporator to a turbine inlet by way of said valve; fluidly interconnecting said evaporator to said actuator such that pressurized refrigerant from said evaporator is selectively caused to move said actuator to open said pneumatically actuated valve.
 12. A method as set forth in claim 11 wherein said pneumatically actuated valve is a normally closed valve.
 13. A method as set forth in claim 11 wherein said actuator includes a vented section and including the step of connecting said vented section to said condenser.
 14. A method as set forth in claim 11 and including the steps of providing a pressure regulator between said evaporator and said actuator and providing pressurized refrigerant to said actuator at a predetermined pressure level.
 15. A method as set forth in claim 11 and including the step of connecting a solenoid valve fluidly between said evaporator and said actuator.
 16. A method as set forth in claim 15 wherein solenoid valve is a three way valve with a vent port and including the step of fluidly connecting said vent to the condenser.
 17. A method as set forth in claim 11 wherein said actuator includes a spring for biasing a sliding piston in position.
 18. A vapor expansion system as set forth in claim 11 wherein said actuator is of the rack-and-pinion type.
 19. A method as set forth in claim 1 and including the step of providing a bypass line for conducting the flow of refrigerant vapor around said turbine and to said condenser by way of a pneumatic valve.
 20. A method as set forth in claim 19 wherein said pneumatic valve is a normally open valve and including the step of fluidly connecting said actuator to said evaporator. 